Another day, another coffee study. New research suggests that coffee can protect your brain — and the roast matters.

Canadian researchers from the Krembil Brain Institute in Toronto tested Starbucks VIA Instant light roast, dark roast and decaffeinated dark roast for compounds known as phenylindanes. That's because they think the compounds, which are the result of the roasting process, are the key to brain health — not necessarily the amount of caffeine.

Phenylindanes prevent two protein fragments common in Alzheimer's and Parkinson's diseases, according to the study published in Frontiers in Neuroscience last month.

"It's the first time anybody's investigated how phenylindanes interact with the proteins that are responsible for Alzheimer's and Parkinson's," Ross Mancini, a research fellow involved in the study, said in a statement.

Dark roast coffee yields the highest quantities of phenylindanes, seemingly making it the best pick for brain health.

However, exactly how beneficial the compounds are is still unknown, Mancini said.

Before you change your drinking habits, coffee studies should be taken with a sip of skepticism. As Howard Bauchner, editor in chief of the medical journal JAMA and The JAMA Network, told USA TODAY in the summer, most coffee studies are association studies, meaning they don't show that coffee is the actual reason for the finding.

"It's interesting but are we suggesting that coffee is a cure? Absolutely not," researcher Donald Weaver, co-director of the Krembil Brain Institute, said in a statement.